Today I found I needed to check my SMS message centre settings on my OnePlus One, but wasn’t able to find the option anywhere in the standard settings.
The solution was to use the phone dialer, enter
*#*#4636#*#* and then this takes you through to a testing information screen with various information menus. Under the “Phone Info” menu, down the bottom of the page, you should see the SMS Message Centre options, labelled “SMSC”.
From here you can update the settings and refresh them if you ever have any issues sending SMS messages. Obviously the specific number to enter will depend on your mobile operator.